Many kinds of mechanical equipment utilize electrical sensors to provide signals for measuring parameters or identifying physical events. More particularly, modern internal combustion engines utilize Electronic Throttle Control (ETC) to adjust the fuel injectors, the engine spark and the amount of airflow through an intake manifold to an intake port of the engine in response to sensor monitored operator variations of the throttle. Such ETC systems provide advantages such as reduced costs, improved simplicity, engine noise reduction, throttle command conditioning for emissions reduction, and/or torque based control functions.
Operator adjustment of the throttle or accelerator is typically accomplished through the use of an accelerator input mechanism, such as a foot pedal, joystick, hand pedal, lever or track ball. The input mechanism is mechanically coupled to sensors that in turn provide control signals having magnitudes indicative of the accelerator position to an ETC microprocessor. In response, the microprocessor generates additional electrical control signals for enabling the hardware of the vehicle engine to provide the operating level indicated by the accelerator.
Multiple input sensors are utilized to sense a particular parameter such as the amount of accelerator depression to improve sensing reliability. Redundancies in the accelerator sensors and associated hardware have become standard in ETC systems with the multiple sensors being processed to ensure secure pedal and throttle signals. Failure or deterioration of any of such sensors can possibly result in inconsistent or inaccurate throttle control. Thus, prior art ETC systems monitor the condition of the accelerator sensors so that corrective action can be taken if a sensor is failing or has failed. The corrective action can include the initiation of a “limp home” mode which results in a dash board warning light indication, reduced vehicle acceleration capability and an immediate trip to a repair facility.
“Correlation Error” is a function of the difference in the instantaneous magnitudes of the control signals from a pair of the foregoing sensors. Some prior art ETC systems monitor and store the correlation error of such sensors only when the accelerator pedal is released, for instance. Thus, a correlation error for these sensors is learned only at one accelerator position such as at idle when the throttle is closed. As a result, only the one correlation error value is monitored by such prior art systems to determine ETC accelerator pedal sensor reliability.
In view of the foregoing, it should be appreciated that it is desirable to provide methods and apparatus for improving the detection and notification that a sensor is failing or has failed. It is desirable to anticipate that a sensor is failing so that corrective action can be taken prior to the performance of the sensor degrading a predetermined amount that results in the previously mentioned undesirable “limp home” operation, for instance. In addition, it is desirable to provide methods and apparatus for learning sensor variations over time and for multiple input mechanism positions to allow the manufacturing tolerances for the sensing system to be less restrictive thus permitting a lower system cost. Furthermore, additional desirable features will become apparent to one skilled in the art from the foregoing background of the invention and the following detailed description of the preferred exemplary embodiments and the appended claims.